Despite the recognized benefits of regular physical activity (PA), older adults are the most inactive segment of the U.S. population, putting them at increased risk for a number of chronic diseases and conditions including cardiovascular disease, diabetes, and weight gain. Efforts to understand the factors influencing physical activity in this important at-risk group have been limited primarily to demographic and psychosocial domains. While an increasing number of individually-adapted interventions have been developed for older adults, few systematic investigations have studied the impacts of objective and subjective environmental factors on physical activity increases within an intervention context. The proposed project takes advantage of the sampling, recruitment, and data collection methods of a recently completed NIH multi-site clinical trial aimed at evaluating the health-related impacts of a physical activity intervention in community-dwelling adults ages 70-89 years (LIFE-P trial). The primary objective of the proposed study is to investigate whether LIFE-P participants'systematic attempts to become more physically active were facilitated or impeded by the walkability of their neighborhood environments after adjusting for study site (San Francisco Bay area, CA, Dallas, TX, Pittsburgh, PA, Winston-Salem, NC) and other variables of interest. Additional questions of interest concern the moderating effects of physical function, SES, health status, and perceived neighborhood cohesion on the environment/ physical activity intervention relationship. The rich LIFE-P dataset includes multiple measurements of key health variables over a 12-month period (e.g., health status, objectively determined and perceived physical functioning, physical activity, quality of life). It will be combined with newly acquired data targeting stable elements of participants'neighborhood environments (including objective macro-scale and observed micro-scale built environment features, and perceived neighborhood variables). This study benefits from the expertise of a multi-disciplinary international team. It will contribute important conceptual and public health information that can inform intervention and policy decisions related to modifying neighborhood environment characteristics to promote physical activity and other health and quality of life outcomes among physically vulnerable older adults-- a group representing a prevalent, sedentary, and under-served segment of the U.S. population. PUBLIC HEALTH RELEVANCE: This study will contribute important conceptual and public health information that can inform intervention and policy decisions related to modifying neighborhood environment characteristics to promote physical activity and other health and quality of life outcomes among physically vulnerable older adults a group representing a prevalent, sedentary, and under-served segment of the U.S. population.